NATURAL PHILOSOPHY. l.')! 



indestructible that approaches this in tlie fidelity with which it re- 

 produces all the attributes of the photog-raph to be preserved, and 

 in the assurance of safety which it affords. And now we come to 

 what is called the carbon process, or carbon printinj^. Is it pos- 

 sible to print a photograph on paper so that it shall be as per- 

 manent as the impression of a steel engraving in printer's ink ? 

 Whatever we may come to hereafter, it is generally accepted at 

 present that if a photographic print is to rival ordinary prints in 

 permanence, this can only be by reproducing it in an ink which, 

 like printer's ink, has carbon for its base. !So there are a great 

 number of ingenious processes for transferring to gradations of 

 carbon the gradations of light and shade which we see in photo- 

 graphs. The essential theory of these processes is suggested by 

 the experiments of M. Niepce, announced in 1827, and of Mr. 

 Mungo Ponten, announced in 1839. There are substances, solu'ole 

 in water, which become insoluble when subjected to the agency 

 of light. If a photographic image be transferred to the surface 

 of such a substance, the light passing through the light parts of 

 the negative, and not through the dark, will so act upon the sur- 

 face that parts of it will wash away, and parts not. The surface 

 when washed will be raised or depressed according to the quantity 

 of light which at different points has acted upon it; and the de- 

 pressions thus contrived will accept a film of carbon, which in its 

 various gradations of thickness will more or less accurately rep- 

 resent the lights and shadows of the photograph. 



Most of the French carbon prints are described as produced by 

 the process of Poitevin, who, in 1855, succeeded in turning to ac- 

 count the discovery of Mr. Mungo Ponten. He combined carbon 

 or any other pigment, in a fine state of division with gelatine, 

 starch, or gum, applied it over the surface of his paper, dried it, 

 submitted it to the action of light under a photographic negative, 

 and so first produced what is now usuiiUy called a carbon print. 

 The chief English exhibitors of carbon printing are Mr. Wood- 

 bury, of London, Mr. Swan, of Newcastle, and Mr. Pouncey, of 

 Dorchester. Among these, as a discoverer, Mr. Pouncey stands 

 first in point of time. His first announcements belong to the 

 year 1858, — that is, three years after Poitevin's first success. 



Mr. Swan, of Newcastle, comes after Mr. Pouncey in point of 

 time : his discovery dates from 1864 ; he appears to have carried 

 his process of carbon printing to a high degree of perfection. 

 The latest process of carbon printing invented in England is that 

 of Mr. Walter Woodbury. It is very simple, and the results arc 

 full of promise. A picture is transferred to a thin sheet of gela- 

 tine ; water washes away those parts of the gelatine on which the 

 light has not acted, and we have are lieved surface which per- 

 fectly represents the light and shadow of the picture. By hydraulic 

 pressure the gradations of relief on the gelatine are transferred 

 to soft metal, and the impressions, which are of much softness 

 and beauty, are produced by mechanical means so simple that 

 thousands of them can be obtained in a few hours. — Druggists' 

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